Multiple-band amplifier

ABSTRACT

A GaAs MMIC dual-band amplifier for wireless communications is disclosed for operation at either the 800 MHz or the 1900 MHz band and it provides desired gain and input and output impedance. Switching impedance networks are used at the input and output of the amplifier to provide matching input impedance and desired output impedance for operation in the two bands. Switching impedance networks are also used between any successive stages of the amplifier to provide proper interstage impedance. The dual band amplifier includes a bias control circuit which biases the amplifier to operate in A, B, AB or C mode. The amplifier can be used for the AMPS 800 or the GSM 900 operation or any other cellular operation such as the PCS 1900 and the it can be switched between the two operations by simply applying a proper control signal to the amplifier.

FIELD OF THE INVENTION

The present invention relates to the field of amplifiers and moreparticularly, power amplifiers for wireless telecommunications.

BACKGROUND OF THE INVENTION

There are currently many different wireless communications systemspromulgated by the telecommunications industries and used in the world.These systems are complex and they set forth specifications regardingall aspects of wireless communications, including physicalcharacteristics of signal transmission, such as transmission frequencyand operation mode.

One of the earliest wireless communications systems developed in NorthAmerica is called the advanced mobile phone service ("AMPS"). Used foranalog cellular communications, AMPS specifies a mobile stationtransmission frequency band between 824 MHz and 849 MHz. This band isoften referred to as the 800 MHz band or the cellular band. Within thesame frequency band also operates a later developed system called thedigital mobile phone service ("DMPS"), which is used for both digitaland analog communications. These systems are generally referred to inthe industry as AMPS 800 and DMPS 800.

A European wireless communications system, the global system for mobilecommunications ("GSM"), specifies a mobile station transmissionfrequency band between 890 MHz to 915 MHz and it is used for digitalcommunications. This system is often referred to as GSM 900. Althoughnot widely adopted in North America, GSM 900 is highly popular in Europeand parts of Asia. Recently, a new system called personal communicationssystem ("PCS") 1900 which specifies a mobile station transmissionfrequency between 1850 MHz and 1910 MHz is proposed for use in NorthAmerica. The transmission frequency of PCS 1900 is substantially higherthan that of AMPS 800 or GSM 800.

There are many other systems. For example, the nordic mobile telephone450 system ("NMT-450") specifies a transmission frequency between 463MHz and 468 MHz and the signal modulation technique of FDMA. The nordicmobile telephone 900 system ("NMY-900") specifies a transmissionfrequency between 935 MHz and 960 MHz and the same signal modulationtechnique.

As for digital cordless telephones, there are, for example, cordlesstelephone 2 ("CT2") requiring a transmission frequency between 864 MHzand 868 MHz and modulation technique of TDMA/FDM, and digital Europeancordless telephone ("DECT") specifying a transmission frequency between1880 MHz and 1990 MHz with the same modulation technique.

Those different transmission frequency bands and operating modes presenta unique challenge for wireless service providers and particularly formanufactures of wireless communications equipment. If a service providerwishes to replace its currently used wireless system with one operatingin a higher frequency band (e.g., from AMPS 800 to PCS 1900), theexisting base stations must be upgraded so that they operate inaccordance with the new system. By using upconverters which convert alower frequency signal to a higher frequency signal, the base stationscan be upgraded to operate at a higher frequency. Of course the basestations must also be updated to comply with other aspects of the newwireless system.

In addition to upgrading the base stations, individual cellulartelephones in the hands of customers must also be upgraded or replacedso that they be compatible with the new wireless system. In particular,since the power amplifier used in each cellular phone is optimized tooperate within a particular frequency band and at a particular mode, itneeds to be replaced with a new power amplifier suitable for operationunder the new wireless standard.

For example, cellular phones used for AMPS 800 contain a power amplifieroptimized to operate within the cellular band (i.e., the 800 MHz band).If, however, AMPS 800 is replaced with PCS 1900, the old AMPS phonescannot be used any more; they must be upgraded or replaced. Replacementof cellular phones is expensive. A new cellular phone which can beeasily upgraded is desired.

For cellular phone manufactures, different wireless systems requiresdifferent power amplifiers, which increases cost. It is desired that asingle amplifier be used for different systems. Different wirelesssystems present another problem: If a cellular phone user crosses fromone area served by one wireless system into an area served by adifferent wireless system, he will not be able to use his phone. It isdesired that the same cellular phone be used under different wirelesssystems and that the user can simply activate a switch to use it under adifferent wireless system. Preferably, when a user enters into an areaserved by a different wireless system, the user's phone is automaticallyswitched to operate under the new wireless system that covers the area.This can be achieved by a base stations sending a signal to the cellularphone to switch the cellular phone. In any event, it requires a poweramplifier capable of operating under different wireless systems.

U.S. Pat. No. 5,060,294 assigned to Motorola Inc. describes a dual modepower amplifier operable in either linear or saturation mode. The modeselection is accomplished with the use of a processor by (1) alteringthe dc bias to a power transistor in the amplifier and/or (2) alteringthe ac load of the amplifier to change the load line. Although theamplifier may operate in either linear or saturation mode, it is notsuitable for operation at different wireless frequencies. For example,the amplifier is not suitable to operate in both the cellular band (the800 MHz band) and the new PCS band (the 1900 MHz band).

U.S. Pat. No. 5,438,684, also assigned to Motorola Inc., describes adual-mode RF signal power amplifier comprising two amplifying branchesconnected in parallel, one for non-linear mode operation such as the FMmode and the other for linear mode operation such as the TDMA digitalmode. A PIN diode is connected in series with one of the branch fordecoupling it from the other branch. When operating, the selected branchis turned on whereas the non-selected branch is turned off. Thisdual-mode power amplifier is only suitable for operation at onefrequency such as 800 MHz or 1900 MHz, but not at both frequencies.

It is therefore an object of the present invention to provide amulti-band amplifier which can operate under different wireless systemsand provide required power and efficiency.

SUMMARY OF THE INVENTION

The present invention provides an amplifying apparatus to operate atdifferent frequencies or in different frequency bands (e.g., cellularband and the PCS band) and in different modes (e.g., A, B, AB or C). Theamplifier can be used in cellular phones to operate under differentwireless systems.

In one embodiment, the amplifying apparatus comprises a plurality ofamplifiers each suitable to operate at one of a plurality ofpredetermined frequencies, and a control circuit. According to thefrequency of input signal, the control circuit, responsive to a controlsignal, selectively enables the amplifier suitable for operating at theinput signal frequency while it preventing the other amplifiers fromoperation. The control signal may be generated manually with the use ofa switch or automatically by a detecting circuit which detects thefrequency of the input signal; it may also be provided or triggered by abase station for wireless communications.

In this embodiment, each amplifier comprises at least one amplifyingstage for amplifying the input signal. Each amplifier has inputimpedance means for providing predetermined input impedance and outputimpedance means for providing predetermined output impedance at thefrequency the amplifier is suitable to operate. Preferably, the inputimpedance approximately matches source impedance of input signal.

In a preferred embodiment, each amplifier comprises a plurality ofamplifying stages arranged as a cascade. Predetermined interstageimpedance between any two successive amplifying stages is provided byinterstage impedance means at the signal frequency the amplifier issuitable to operate. Preferably, each amplifier stage includes at leastone amplifying transistor, and the amplifier is enabled or disabled bythe control circuit by turning the amplifying transistor(s) in theamplifier on or off. The control circuit also operates to bias theselected amplifier to operate in a desired operating mode. Morepreferably, the amplifying apparatus comprising the amplifiers and thecontrol circuit is a monolithic GaAs integrated circuit ("GaAs MMIC").

In accordance with another embodiment, an amplifying apparatus isprovided with at least one amplifying stage, and input impedance meansfor providing, in accordance with the frequency of input signal,predetermined input impedance at the frequency of the input signal.Preferably, such input impedance matches source impedance. Morepreferably, the amplifying apparatus further includes output impedancemeans for providing predetermined output impedance at the signalfrequency. Still more preferably, a bias control circuit is provided forselectively biasing the amplifying stage to operate in one of aplurality of predetermined operating modes.

In a preferred embodiment, the amplifying apparatus includes a pluralityof amplifying stages arranged as a cascade. The apparatus is providedwith input impedance switching means which selectively provides, inaccordance with input signal frequency, one of a plurality of inputimpedance networks to input of a first amplifying stage. Operating withthe first stage, the selected input impedance network providespredetermined input impedance which preferably approximately matchessource impedance at the input signal frequency. Interstage impedancemeans are also provided for providing predetermined interstageimpedance. More specifically, the interstage impedance means comprisemeans for controlling, in accordance with the input signal frequency,the impedance of an impedance network connected between a proceedingstage and a dc power supply.

The preferred embodiment is further provided with output impedanceswitching means which selectively provides, in accordance with inputsignal frequency, one of a plurality of output impedance networks tooutput of a last amplifying stage. Operating with the last stage, theselected output impedance network provides predetermined outputimpedance.

BRIEF DESCRIPTION OF THE DRAWINGS

Those and other objects, features and advantages of the invention willbe more apparent from the following detailed description in conjunctionwith the appended drawings in which:

FIG. 1A is the block diagram of a multi-band amplifier of the presentinvention;

FIG. 1B is the block diagram of another multi-band amplifier of thepresent invention;

FIG. 2 is the block diagram of a preferred embodiment of a multi-bandamplifier of the present invention;

FIGS. 3A and 3B is a schematic-block diagram of a GaAs MMIC inaccordance with the present invention which is used to form themulti-band amplifier of FIG. 2;

FIG. 4 is the block diagram of another embodiment of a multi-bandamplifier of the present invention;

FIGS. 5A-E are block diagrams of alternative embodiments of a multi-bandamplifier of the present invention;

FIG. 6A is the block diagram of a preferred embodiment of a multi-stage,multi-band amplifier of the present invention;

FIG. 6B is a schematic-block diagram of the amplifier of FIG. 6A;

FIG. 7A is the block diagram of an alternative embodiment of amulti-stage, multi-band amplifier of the present invention;

FIG. 7B is a schematic-block diagram of the amplifier of FIG. 7A;

FIG. 8 is the block diagram of a preferred embodiment of a multi-stage,multi-band amplifier of the present invention;

FIG. 9 is the block diagram of an alternative embodiment of theamplifier depicted in FIG. 8;

FIG. 10 is the schematic circuit diagram of a GaAs MMIC of the presentinvention which is used to form the multi-band amplifier of FIGS. 8 and9;

FIG. 11 is the schematic circuit diagram of a preferred embodiment of abias control circuit of the present invention;

FIG. 12 is the schematic circuit diagram of a preferred embodiment of acontrol circuit of the present invention; and

FIG. 13 is a block diagram showing an alternative way to providepredetermined output impedance in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a multi-band amplifier with high powerand efficiency for wireless or other applications where a multi-bandamplifier is required.

Upon examining existing amplifiers prior to the present invention, theinventor of the present invention found that there are two mainobstacles for developing a wide band power amplifier that can operateunder different wireless systems over a broad band (such as a bandcovering the frequency range from 800 MHz to 1900 MHz):

First, changing from one wireless system to another wireless systemoften changes the transmission frequency, resulting in changes of input,output and inter-stage impedance of an amplifier. The changes of theseimpedance, which had been optimized to operate at a prior frequencyband, destroys the optimized condition, resulting in reduced gain, powercapability and efficiency. Second, different wireless systems oftenrequire the amplifiers to operate in different modes (e.g., A, B, AB orC). The operation mode of an amplifier is set by providing a proper biasto the transistors in the amplifier and by providing a proper ac loadline. Most of the existing amplifiers can only operate in one mode whichis fixed when the amplifier is made.

A conventional amplifier is designed to operate at a particularfrequency or within a particular frequency band. At such frequency, theamplifier provides input impedance that matches source impedance, andoutput impedance of a desired value. For example, the source impedanceis typically 50 ohms. The output impedance can be 5 ohms. The factorsconsidered in determining the desired output impedance are mainly (1)the frequency at which the amplifier is to operate, (2) the output powerthat the amplifier is to provide, and (3) the dc bias to the amplifier.

If the amplifier contains more than one amplifying stage, properinterstage impedance between two successive stages is also required.Preferably, the interstage impedance is such that matching impedancebetween adjacent stages is provided (i.e., the output impedance of aproceeding stage matches the input impedance of a following stage),which maximizes the output power level. Moreover, the interstageimpedance is such that it provides a suitable interstage load line for adesired mode of operation. For the 800 MHz operation, because the acgain of an amplifier is more readily obtained, stringent interstageimpedance matching is usually not required. The amplifier typicallyprovides sufficient gain as long as the impedance between two successivestages is not overly mismatched. For higher frequency operation such asthe 1900 MHz operation, however, more stringent interstage impedancematching is required in order to achieve required output power level.Preferably, impedance matching is achieved between adjacent stages forhigh frequency operations.

When an amplifier is put to operate at a substantially differentfrequency than it is originally designed, the input and output impedanceof the amplifier and any interstage impedance changes due to thefrequency change. As a result, the amplifier no longer provides matchinginput impedance. The output impedance of the amplifier also changes. Ifthere was matching interstage impedance at the original frequency, itwill no longer exist at the new frequency. The amplifier will generallyno longer provide the required ac gain, output power level andefficiency. For example, a conventional 800 MHz power amplifier wouldnot properly operate at 1900 MHz.

The present invention provides an amplifying apparatus which operates atdifferent frequencies and in different modes. Referring to FIG. 1A, in afirst embodiment, amplifying apparatus 10 of the present inventioncomprises a first amplifier 20, a second amplifier 30 and a controlcircuit 40. Depending on input signal frequency, control circuit 40selectively enables one of the two amplifiers to operate while preventsthe other amplifier to operate.

First amplifier 20 is suitable to operate at a first frequency f₁ (e.g.,800 MHz) or in a first frequency band (e.g., the cellular band). Itcomprises an amplifying stage 22, an input impedance network 24 and anoutput impedance network 26. Input signal 29 at first frequency f₁ isprovided to an input terminal 27, and output signal from the amplifieris provided at an output terminal 28. In this amplifier, input impedancematching source impedance is provided at around frequency f₁ by inputimpedance network 24 operating in conjunction with amplifying stage 22.Predetermined output impedance is obtained at around frequency f₁ byoutput impedance network 26 operating in conjunction with amplifyingstage 22.

Second amplifier 30 is suitable to operate at around a second frequencyf₂ (e.g., 1900 MHz) or in a second frequency band (e.g., the PCS band).It comprises an amplifying stage 32, input impedance networks 34 andoutput impedance network 36. Input signal 39 is received at an inputterminal 37. Output signal from amplifier 30 is provided at an outputterminal 38. In amplifier 30, input impedance matching source impedanceis provided at around frequency f₂ by input impedance network 34operating in conjunction with amplifying stage 33. Predetermined outputimpedance is obtained at frequency f₂ by output impedance network 36operating in conjunction with amplifying stage 32.

Control circuit is connected to amplifiers 20 and 30. It receivescontrol signal 41 and selectively enables, in accordance with thecontrol signal, the amplifier suitable for operating at the frequency ofthe input signal while prevents the other amplifier from operation.

Amplifying apparatus 10 operates as follows: If the input signal is atthe first frequency (e.g., 800 MHz), it is provided to the firstamplifier. Control circuit 40, responsive to control signal 41, enablesfirst amplifier 20 to operate while prevents second amplifier 30 fromoperation. Input signal 29 is thus amplified by first amplifier 20. Ifthe input signal is at the second frequency (e.g., 1900 MHz), the inputsignal is provided to second amplifier 30. Control circuit 40 enablessecond amplifier 30 while disables first amplifier 20, and the inputsignal is amplified by second amplifier 30. In this way, the amplifyingapparatus operates on a signal having any of the two predetermined,different frequencies.

The selectively providing the signal to the first or second amplifier inaccordance with signal frequency can be accomplished in many differentways. For example, in the context of cellular communications, it can beaccomplished by a base station sending signal to a cellular phoneindicating the frequency of the incoming signal; the cellular phone thensends a control signal to a switching circuit which directs the incomingsignal to the appropriate amplifier. The same control signal alsotriggers the control circuit to enable the appropriate amplifier.

Referring to FIG. 1B, a switch circuit 43 is used to selectively provideinput signal 45 to amplifier 20 or 30. Illustratively, switch circuit 43includes a switch 44 responsive to control signal 41. If incoming signal45 is at the first frequency, control signal 41 commands switch 44 toprovide the incoming signal to first amplifier 20; it also triggerscontrol circuit 40 to enable first amplifier 20 and to disable secondamplifier 30. Conversely, if the incoming signal is at the secondfrequency, the incoming signal is provided to second amplifier 30, andsecond amplifier 30 is enabled. Preferably, first amplifier 20, secondamplifier 30, and bias control circuit 40 are formed as a monolithicintegrated circuit and more preferably, a GaAs MMIC.

The term "frequency" used here refers to both individual frequencies andfrequency bands. For example and without limitation, the first amplifieris suitable to operate in the 800 MHz band and the second amplifier issuitable to operate in the 1900 MHz band. An amplifying apparatuscapable of operating in different frequency bands is within the scope ofthe present invention.

Referring to FIG. 2, a part-block and part-schematic diagram, apreferred amplifying apparatus 50 comprises a first amplifier 60 foramplifying the 800 MHz signal, a second amplifier 80 for the 1900 MHzsignal and a bias control circuit 100.

First amplifier 60 comprises three amplifying stages 62, 64 and 66arranged as a cascade. An impedance network 68 is connected to the inputof first stage 62, and it operates with first stage 62 to providematching impedance to input 800 MHz signal 67. Between first and secondamplifying stages 62 and 64, there is connected an impedance network 70which provides, in conjunction with an inductor 76, predetermined properimpedance between first stage 62 and second stage 64 for 800 MHzoperation. Coupled between second stage 64 and third stage 66 is animpedance network 72 which provides, in conjunction with anotherinductor 76, proper predetermined impedance between second stage 64 andthird stage 66 for the 800 MHz operation. The output of third stage 66is connected to an impedance network 74 which operates with third stage66 and an inductor 76 to produce predetermined, desired load impedancefor the 800 MHz operation.

Amplifying stages 62, 64 and 66 are powered by a dc power supply +V_(DD)through three choke inductors 75, 76 and 79, and an off-chip, on/offswitch 77. Three capacitors 81, 83 and 85 are used to provide ac groundto the power supply. Inductors 75, 76 and 79 will effect the interstageimpedance and the output impedance. If the inductance of inductors 75,76 and 79 is large, however, their effect on the interstage impedanceand the output impedance is negligible.

Second amplifier 80 for amplifying the 1900 MHz signal comprises threecascade amplifying stages 82, 84 and 86. The input of amplifying stage82 is connected to an impedance network 88 which operates withamplifying stage 82 to provide impedance that matches source impedancefor the 1900 MHz operation. At the output of third amplifying stage 86,an impedance network 94 operates with third stage 86 and an inductor 97to provide predetermined, desired output impedance for the 1900 MHzoperation. Impedance networks 90 and 92 and inductors 95, 96 and 97provide predetermined, desired inter-stage impedance for 1900 MHzoperation. Preferably, the impedance value of network 90 at 1900 MHz issuch that matching impedance between stages 82 and 84 is achieved.Similarly, the impedance of impedance network 92 is such that matchingimpedance between amplifying stages 84 and 86 are obtained at around1900 MHz. Second amplifier 80 is also powered by the dc power supply+V_(DD) through a switch 77 and three choke inductors 96. Capacitors 98,99 and 101 are used to provide AC ground to the power supply.

Bias control circuit 100 is connected to both amplifiers 60 and 80. Inaddition to selectively enabling one of amplifiers 60 and 80 to operatewhile preventing the other amplifier from operation, control circuit 100also provides a predetermined bias to the selected one amplifier to biasit to a desired mode of operation. Bias control circuit 100 is connectedto a switch 108 at a terminal 102 for receiving a control signal. Apositive power supply V_(DB) is provided to control circuit 100 at aterminal 104, and a negative dc power supply V_(SS) is provided tocontrol circuit 100 at a terminal 106.

Amplifying apparatus 50 operates as follows: For 800 MHz operation,switch 108 is connected to terminal 110 at which a reference voltage for800 MHz operation is provided. Responsive to this reference voltage,bias control circuit 100 provides a negative voltage to three amplifyingstages 82, 84 and 86 in the second amplifier to turn off these stages.At the same time, a proper bias is provided to amplifying stages 62, 64and 66 for them to operate in a desired mode. The amplifying apparatusis thus ready for 800 MHz operation.

For 1900 MHz operation, switch 108 is connected to terminal 112 where areference voltage for 1900 MHz operation is provided. In response to thereference voltage, bias control circuit 100 provides a negative bias toturn off the amplifying stages in first amplifier 60. A desired bias forthe 1900 MHz operation is provided to second amplifier 80 by biascontrol circuit 100.

Preferably, a portion 114 of amplifying apparatus 50 is in the form of aGaAs monolithic microwave integrated circuit ("MMIC"). More preferably,depletion-mode GaAs field effect transistors are used for signalamplification.

FIGS. 3A and 3B together illustrate a part-schematic circuit, part-blockdiagram of a preferred embodiment of the multi-band amplifier of FIG. 2.In each amplifier, the first two amplifying stages includes a depletionmode GaAs MESFET, and the last stage includes two depletion mode GaAsMESFETs for improved output power level. It will be apparent to one ofskill in the art that there are numerous alternative ways to form theamplifying apparatus of FIG. 2; the circuit depicted in FIGS. 3A and 3Bis merely an example and not a limitation.

In accordance with a second embodiment of the present invention, anamplifying apparatus is provided with at least one amplifying stage andinput impedance means. The input impedance means provide, in accordancewith the frequency of input signal, predetermined input impedance at thefrequency of the input signal. Preferably, such predetermined inputimpedance is the impedance that matches source impedance. (Sourceimpedance is the impedance of the signal source.)

The amplifying apparatus further includes output impedance means forproviding, in accordance with the frequency of the signal, predeterminedoutput impedance at the frequency of the input signal. In addition, acircuit for selectively biasing the amplifying stage to operate in apredetermined mode is also provided.

An example of this second embodiment is shown in a block diagram of FIG.4. An amplifying apparatus 150 includes a single amplifying stage 152having an input node 154 and an output node 156. Input node 154 isconnected to a switch 158 which is selectively connected to either inputimpedance network 160 or 162. Output node 156 is connected to a switch164 for selectively coupling to either output impedance network 166 or168.

Input signal 174 of a first frequency (e.g., 800 MHz) is received by theamplifying apparatus at a terminal 170 connected to impedance network160. Input signal of a second frequency (e.g., 1900 MHz) is received ata terminal 172 connected to impedance network 162. For simplicity, 800MHz and 1900 MHz are used here to represent the 800 MHz cellular bandand the 1900 MHz PCS band; they are also referred here as the 800 MHzoperation and the 1900 MHz operation. It will be apparent to one ofskill in the art that these two frequencies are merely illustrative--theamplifying apparatus of the present invention can be adapted to operateat other frequencies or frequency bands, or at more than twofrequencies, which are all within the scope of the present invention.

Amplifying apparatus 150 provides output signal at 800 MHz, through anoutput impedance matching network 168, at output terminal 178. A 1900MHz output signal is provided, through output impedance network 166, atan output terminal 180. Amplifying apparatus 150 receives dc power froma dc power supply +V_(DD) through an impedance network 182. A biascontrol circuit 184 is used to selectively bias the amplifying stage tooperate in a desired mode. For example, amplifying stage 152 can bebiased for class A, B, AB or C operation.

Predetermined impedance for 800 MHz operation is provided by impedancenetworks 160, 168 and 182 in conjunction with amplifying stage 152. Morespecifically, input impedance networks 160 operating in conjunction withamplifying stage 152 provides input impedance that approximately matchessource impedance at 800 MHz. Predetermined output impedance is providedfor the 800 MHz operation by output impedance network 168 in conjunctionwith amplifying stage 152 and impedance network 182. If the impedance ofnetwork 182 is large (such as a large choke inductor), its effect on theoutput impedance is negligible and the output impedance of amplifyingapparatus 150 is mainly determined by output impedance network 168 andamplifying stage 152.

Similarly, for the 1900 MHz operation, proper impedance is provided byimpedance networks 162, 166 and 182 in conjunction with amplifying stage152. Input impedance matching source impedance at 1900 MHz is obtainedby impedance network 162 operating in conjunction with amplifying stage152. Predetermined output impedance for the 1900 MHz operation isachieved by impedance networks 166 and 182 operating in conjunction withamplifying stage 152.

The term "impedance network" or "impedance matching network" is usedhere to refer to any electronic component or circuit thereof thatdisplays a predetermined impedance at a frequency. It includes, withoutlimitation, passive components, such as capacitors, resistors andinductors, and active components, such as transistors, diodes andcircuits thereof.

Amplifying apparatus 150 operates as follows: For the 800 MHz operation,the input of amplifying stage 152 is connected to impedance network 160,and the output of the amplifier is connected to impedance network 168. Adesired bias is provided to amplifying stage 152 by bias circuit 184. Ifthe input signal is at 1900 MHz, impedance networks 162 and 166 areconnected to the input and output of amplifying stage 152, respectively,and a desired bias for the 1900 MHz operation is provided to amplifyingstage 152 by bias circuit 184.

It will be apparent to one of ordinary skill in the art that, althoughFIG. 4 depicts a dual-band amplifier, an amplifying apparatus for morethan two bands can also be provided in accordance with the presentinvention, which is within the scope of the present invention.

It will also be apparent to one of ordinary skill in the art that theessence of the present invention is to provide predetermined input andoutput impedance and predetermined bias to the amplifier for differentfrequency operations. The embodiment of FIG. 4 illustrates an examplefor providing predetermined input and output impedance for differentfrequency operations by using switching input impedance networks andswitching output impedance networks. As will be appreciated by one ofskill in the art, there will be numerous ways to provide, in accordancewith the present invention, predetermined input and output impedanceaccording to the signal frequency, which are all within the scope of thepresent invention. Some of the alternative embodiments of the presentinvention will now be described below.

FIG. 5A is the block diagram of an alternative embodiment wherein likeelements are similarly designated as FIG. 4. For the 800 MHz operation,switches 190 and 194 are closed, and switches 192 and 196 are open. Forthe 1900 MHz operation, switches 192 and 196 are closed and switches 190and 194 are open.

FIG. 5B illustrates another alternative embodiment. Amplifying stage 152is coupled to the dc power supply +V_(DD) through one of two outputimpedance networks 198 and 200 by a switch 202. An impedance network 204is connected to the output of the amplifying stage. Predetermined outputimpedance at 800 MHz is provided by connecting a switch 202 to impedancenetwork 198 for the 800 MHz operation. For the 1900 MHz operation,predetermined output impedance at 1099 MHz is provided by connectingswitch 202 to impedance network 200.

It should be noted that in this embodiment, predetermined outputimpedance for different frequency applications is obtained by switchablyconnecting impedance network 198 or 202 to the power supply. As is wellknown to those of skill in the art, an impedance component connected tothe dc power supply in the shown fashion has a direct effect on theoutput impedance of the amplifying stage. Clearly, the impedance valuesfor impedance networks 198, 200 and 204 need to be such that desiredoutput impedance for the 800 MHz or 1900 MHz operation is provided.

FIG. 5C is a block diagram depicting yet another way of providingpredetermined input and output impedance for different frequency orfrequency band operations. In this embodiment, input of amplifying stage152 is connected to two impedance networks 208 and 210 connected inseries. A switch 206 is connected across impedance network 210 and whenclosed, it shorts network 210. Similarly, the output of amplifying stage152 is connected to two impedance networks 214 and 216 connected inseries, with a switch 212 connected across network 214.

This amplifying apparatus operates as follows: Both switches 206 and 212are open for the 800 MHz operation. At an input terminal 218,predetermined input impedance (e.g., about 50 ohms), preferably matchingthe source impedance, is provided by impedance networks 208 and 210operating in conjunction with amplifying stage 152. At an outputterminal 217, predetermined output impedance (e.g., about 5 ohms) isprovided by impedance networks 214 and 216 operating in conjunction withamplifying stage 152 and impedance network 182. If impedance network 182has a large impedance, its effect on the output impedance is negligibleand the output impedance is mainly determined by networks 214 and 216and amplifying stage 152.

Both switches 206 and 212 are closed for the 1900 MHz operation,shorting impedance networks 210 and 214. Under this configuration,predetermined input impedance (e.g., about 50 ohms) is maintained ataround 1900 MHz by impedance network 20 and amplifying stage 152.Predetermined output impedance (e.g., about 5 ohms) is maintained byimpedance networks 216 and 182 and amplifying stage 152. One advantageof this amplifying apparatus over the previously described ones is thatit requires only a single input terminal and a single output terminalfor both the 800 MHz and the 1900 MHz operations. If one desires, inputimpedance networks 208 and 210 can be such that predetermined, differentinput impedance for the 800 MHz and 1900 MHz operations be obtained.Similarly, predetermined, different output impedance for the 800 MHz and1900 MHz operations can also be obtained.

FIG. 5D depicts another alternative embodiment wherein two pairs ofswitching impedance networks are used for providing desired,predetermined output impedance for different frequency operations.Specifically, for the 800 MHz operation, a switch 158 is connected to animpedance network 160 which, in conjunction with amplifying stage 152,provides predetermined input impedance for the 800 MHz operation. Toprovide predetermined output impedance, a switch 226 connects to animpedance network 218 and a switch 228 connects to an impedance network222; impedance networks 218 and 222 provide, with the amplifying stage,predetermined output impedance for the 800 MHz operation. For the 1900MHz operation, switch 158 connects to an impedance network 162, switch226 connects to an impedance network 22, and switch 228 connects to animpedance network 224; the impedance values of these networks are suchthat desired input and output impedance is provided for the 1900 MHzoperation.

In accordance with the present invention, frequency filters/impedancenetworks are also used in providing predetermined input and outputimpedance for different frequency operations. By example and notlimitation, as illustrated in FIG. 5E, a low-pass filter/impedancenetwork 230 and a high-pass filter/impedance network 166 are connectedto the output of amplifying stage 152. For the 800 MHz operating,low-pass filter/impedance network 230 allows 800 MHz signal to passthrough and provides predetermined output impedance within the 800 MHzband. When the signal is 1900 MHz, it passes through high-passfilter/impedance network 232, which provides predetermined outputimpedance within the 1900 MHz band. Low pass and high pass filters canalso be used in a similar fashion at the input end of the amplifyingstage (not shown), which is within the scope of the present invention.

The amplifying apparatus described thus far contains a single amplifyingstage. For a multiple stage amplifier, in addition to providingpredetermined input impedance and output impedance, it is also requiredthat proper impedance between successive stages be provided. Preferably,the output impedance of a proceeding stage approximately matches theinput impedance of a following stage. For the 800 MHz operation,impedance matching between stages is not critical since sufficient gainis easily obtained even without interstage impedance matching. In fact,interstage impedance mismatching may be desired in certain instances toreduce the gain. For the 1900 MHz operation, however, because the gainis more difficult to achieve, impedance matching between stages isimportant. In accordance with the present invention, predeterminedimpedance between successive stages of an amplifier is provided fordifferent frequency operations.

FIG. 6A is a block diagram of a multi-stage amplifying apparatus 240 inaccordance with the present invention. The apparatus includes threeamplifying stages: a first stage 242, a second stage 244, followed by anoutput stage 246. Connected to the input of first amplifying stage 242is a switch 249, which switchably connects to an impedance network 248or 250. For the 800 MHz operation, switch 249 connects to impedancenetwork 248 which operates in conjunction with first amplifying stage242 to provide predetermined input impedance. Switch 249 connects toimpedance network 250 for the 1900 MHz operation which operates inconjunction with first amplifying stage 242 to provide desired inputimpedance for the 1900 MHz operation. Preferably, the input impedanceprovided by impedance network 248 or 250 is about 50 ohms to matchsource impedance.

Proper interstage impedance between first and second stages is providedwith the use of switches 255 and 261 and impedance networks 254, 256,260 and 262. For the 800 MHz operation, switch 255 connects to network254 which, together with impedance network 252 and first amplifyingstage 242, provides predetermined interstage impedance suitable for the800 MHz operation. Switch 255 connects to impedance network 256 for the1900 MHz operation, which, together with impedance network 252 and firstamplifying apparatus 242, provides predetermined interstage impedance.Preferably, for the 1900 MHz operation, the output impedance of firststage 242 approximately matches the input impedance of second stage 244.Similarly, predetermined interstage impedance between second amplifyingstage 244 and third amplifying stage 246 is provided by connectingswitch 261 to impedance network 260 for the 800 MHz operation, or toimpedance network 262 for the 1900 MHz operation.

FIG. 6B is a part-block and part-schematic diagram depicting a morepreferred embodiment of the amplifying apparatus of FIG. 6A. Likeelements in this drawing are similarly designated as in FIG. 6A. Twodepletion mode GaAs FETs 270 and 272 are used to form a switch 249, andthey are controlled by proper voltages applied to their gate terminals.For the 800 MHz operation, FET 270 is turned on and FET 272 is turnedoff. Conversely, for the 1900 MHz operation, FET 270 is turned off andFET 272 is turned on. Although this embodiment uses two depletion modeGaAs FETs 270 and 272 to form switch 249, it will be apparent to one ofordinary skill in the art that other devices such as PN diodes, Schottkydiodes, or preferably, PIN diodes can be used instead of the GaAs FETsto form the switch, which are all within the scope of the presentinvention.

An output stage 246 includes two depletion mode GaAs FETs connected inparallel. The drain terminals of the two FETs are biased by a dc powersupply +V_(DD) through one of two inductors 82 and 90, which isselectively connected to the drain terminals by a switch 265. This twoFET type stage provides improved output power capability.

Illustratively, depletion mode GaAs FETs are used as amplifyingtransistors in all three stages. It will be apparent to one of skill inthe art that other kinds of transistors such as bipolar transistors orenhancement mode GaAs FETs can be used instead of the GaAs FETs, whichare all within the scope of the present invention.

FIG. 7A is the block diagram of another alternative embodiment of theamplifying apparatus of FIG. 6A. The output stage of this embodimentincludes two substages 282 and 284 for the 800 MHz or 1900 MHzoperation, respectively. Depending on the frequency of operation, onlyone of the two substages is selectively activated and the selection ismade by a switch 268. For the 800 MHz operation, switch 268 is connectedto substage 282 which provides predetermined output impedance at itsoutput while substage 284 is turned off. Switch 268 connects to substage284 for the 1900 MHz operation, which provides proper output impedancefor the 1900 MHz operation while substage 282 is turned off.

FIG. 7B is a part-block and part-schematic diagram of a more preferredembodiment of the amplifying apparatus of FIG. 7A. Note that two FETs290 and 292 are used as a switch for the output stage. By applyingappropriate gate bias voltages V_(G1) and V_(G2), a desired substage isselected. For example, for the 800 MHz operation, substage 284 iselectrically disconnected from the second stage by applying a gate biasV_(G2) of a negative voltage sufficient to turn off FET 292. In themeantime, substage 282 is electrically connected to the second stage bya gate bias V_(G1) which turns on FET 290. Conversely, for the 1900 MHzoperation, substage 282 disconnected by turning off FET 290 and substage284 is selected by turning on FET 292.

FIG. 8 depicts the block diagram of a preferred multi-band amplifyingapparatus 300 of the present invention. Amplifying apparatus 300includes a GaAs MMIC power amplifier chip 302 and a number of off-chipcomponents. In the GaAs power amplifier chip, three amplifying stages304, 306 and 308 are connected as a cascade through impedance networks310 and 312. A switch 316 is connected to the input of first stage 304through an impedance network 314 and it selectively connects to eitheran impedance network 318 or an impedance network 320. Impedance network318 receives input 800 MHz signal at a terminal 322. Impedance network320 receives input 1900 MHz signal at a terminal 324. When switch 316connects to impedance network 318, predetermined input impedance for the800 MHz operation is provided at input terminal 322. Switch 316 connectsto impedance network 320 for the 1900 MHz operation; impedance network320 operates with first stage 304 to provide predetermined inputimpedance for the 1900 MHz operation.

Two switching impedance networks are used to provide predeterminedoutput impedance for the 800 MHz or 1900 MHz operation. Morespecifically, the output of the third stage is connected to an off-chipswitch 328, which is selectively connected to either an off-chipimpedance network 330 for the 800 MHz operation or an off-chip impedancenetwork 332 for the 1900 MHz operation. The output of the third stage isalso connected to an off-chip impedance network 326 to receive the dcpower +V_(DD). When switch 328 connects to impedance network 330,predetermined output impedance for the 800 MHz operation is provided ata terminal 334 by impedance networks 330 and 326 operating inconjunction with third stage 308. For the 1900 MHz operation, switch 328is connected to impedance network 332 and predetermined output impedanceis provided at terminal 336 by impedance networks 332 and 326 operatingin conjunction with third stage 308.

Predetermined inter-stage impedance for different frequency operationsis obtained in this amplifying apparatus by using switching impedancenetworks. More specifically, first stage 304 is connected to the dcpower supply +V_(DD) via an on-chip impedance network 340 and anoff-chip impedance network 342. Connected across impedance network 340is an on-chip electronic switch 338 which, if closed, shorts impedancenetwork 340. For the 800 MHz operation, switch 338 is open andpredetermined, proper interstage impedance between first amplifyingstage 304 and second amplifying stage 306 for the 800 MHz operation isprovided by impedance networks 310, 340 and 342.

When the apparatus operates within the 1900 MHz band, switch 338 isclosed, shorting impedance network 340. At this time, predetermined,proper interstage impedance between first amplifying stage 304 andsecond stage 306 is provided by impedance networks 342 and 310.Preferably, the impedance values of impedance networks 342 and 310 aresuch that matching impedance between the first and second stage isobtained for the 1900 MHz operation.

Predetermined inter-stage impedance between second amplifying stage 306and third amplifying stage 308 for the 800 MHz or 1900 MHz operation issimilarly obtained with the use of on-chip impedance networks 312 and344, an on-chip electronic switch 348 and an off-chip impedance network346. Switch 348 is open for the 800 MHz operation, and it is closed forthe 1900 MHz operation.

GaAs MMIC power amplifier chip 302 further includes an on-chip controlcircuit 350 for controlling electronic switches 316, 338 and 348. In thefigure, the dash lines connecting these switches to control circuit 350illustrate the control of these switches by control circuit 350. For the800 MHz operation, responding to a control signal V_(C) received from anoff-chip source, control circuit 350 causes switch 316 to connect toimpedance network 318, and opens switches 338 and 348. For the 1900 MHzoperation, it causes switch 316 to connect to impedance network 320, andcloses switches 338 and 348. Control signal V_(c) triggers the controlcircuit to generate proper signals to control those switches; it can be,by example and not limitation, a signal responsive to a cellular basestation.

GaAs MMIC power amplifier chip 302 further includes a bias controlcircuit 352 for providing appropriate bias to amplifying stages 304, 306and 308. For example, depending on the particularly PCS system underwhich the amplifying apparatus is to be used, amplifying stage 304, 306and 308 can be biased for A, B, AB or C operation. Bias control circuit352 is connected to a number of off-chip voltages: a positive voltagesupply V_(DB), a negative voltage supply V_(SS), and a reference voltageV_(REF). Reference voltage V_(Ref) is provided to bias control circuit352 through a switch 354. Bias control circuit 352 can also be connectedto two pairs of optional bias resistors through two off-chip electronicswitches 356 and 358. The optional bias resistors are used to form, withon-chip resistors, a voltage divider by which the bias voltage can beadjusted by judiciously choosing the resistance values of these optionalbias resistors.

Referring to FIG. 9, in an alternative embodiment, the output of thirdamplifying stage 308 is connected to a low-pass impedance network 360and a high-pass impedance network 362. The 800 MHz signal will pass thelow-pass impedance network which provides predetermined output impedancefor the 800 MHz operation. The 1900 MHz signal will pass the high-passimpedance network 362 which provides predetermined output impedance forthe 1900 MHz operation.

FIG. 10 is a partial schematic circuit diagram of a preferred GaAs MMICcircuit 302 of FIG. 8., excluding control circuit 350 and bias controlcircuit 352. (The schematic circuit diagram for the preferred biascontrol circuit is shown in FIG. 11, and the schematic circuit diagramfor the preferred control circuit is shown in FIG. 12.) This preferredGaAs MMIC includes three amplifying stages: a first stage including adepletion-mode GaAs power FET 600, a second stage including adepletion-mode GaAs power FET 602, and a third stage including twodepletion-mode GaAs FETs 604 and 606 connected in parallel. Two inputsignals, 800 MHz signal and 1900 MHz signal, are provided at terminals608 and 610, respectively. Two depletion-mode GaAs FETs 612 and 614,controlled by a control circuit (shown in FIG. 12), function toselectively provide either the 800 MHz signal or the 1900 MHz signal tothe first amplifying stage. The control circuit applies appropriatecontrol voltages V_(C1) and V_(C2) through conductors 616 and 618 to thegate of FETs 612 and 614 to cause the FETs to turn on or off. Thecontrol circuit also control FETs 620 and 622 which function as switchesfor providing predetermined inter-stage impedance.

GaAs power FETs 600, 602, and 604 and 606 are biased by a bias controlcircuit (shown in FIG. 11) at terminals 624, 626 and 628. Bias voltagesapplied to the three terminals are designated as V_(G1), VG_(G2) andVG_(G3).

By example and not limitation, FIG. 11 is a schematic circuit diagram ofa preferred bias control circuit 623. Bias control circuit 623 comprisesthree depletion mode GaAs FETs 630, 632 and 634. A positive dc powersource +V_(DB) and a negative power source -V_(SS) are connected to thebias control circuit. A reference voltage V_(Ref) is also applied to thegate of FET 632. Bias circuit 623 provides a bias voltage at a terminal363 that is connected to the amplifying circuit of FIG. 10 at terminals624 (V_(G1)), 626 (V_(G2)) and 628 (V_(G3)). The amplitude of the biasvoltage generated at terminal 636 is controlled by the reference voltageV_(Ref) and it is between the positive power supply voltage +V_(DB) andthe negative power supply voltage -V_(SS). By applying appropriatereference voltage V_(Ref), a desired bias voltage is obtained.Preferably, bias control circuit 623 is a part of a GaAs MMIC whichincludes the amplifying circuit of FIG. 10 and the bias control circuitof FIG. 11. It will be apparent to one of ordinary skill in the art thatother bias circuits different from the one depicted in FIG. 11, can alsobe used in place of bias control circuit 623 described above.

Referring to FIG. 12, by way of example and not limitation, a controlcircuit 640 is connected to ground at a terminal 644 and to a negativepower source -V_(SS) at a terminal 642. An external control voltageV_(C) is provided to the control circuit at a terminal 646. Controlvoltages V_(C1) and VC_(C2) are provided at terminals 648 and 650,respectively. Preferably, control circuit 640 is formed with amplifyingcircuit 302 depicted in FIG. 10 and bias control circuit 623 depicted inFIG. 11 as a GaAs MMIC.

Referring to both FIG. 10 and FIG. 12, control circuit 640 operates asfollows: When V_(C) is a low voltage such as ground, V_(C1) is low andV_(C2) is high and as a result, amplifying circuit 302 is set up for the800 MHz operation. Conversely, if V_(C) is high, then V_(C1) becomeshigh and V_(C2) is low; amplifying circuit 302 is ready for the 1900 MHzoperation.

It will be apparent to one of ordinary skill in the art that othercircuits different from the control circuit depicted and describedherein may also be used in place of the control circuit, as long as theyprovide appropriate control voltages.

FIGS. 13 illustrates an alternative ways for providing predeterminedoutput impedance for different frequency operations. For simplicity,only the last stage is illustrated. Last stage 652 is connected to twoimpedance networks 654 and 656. Capacitors 658 and 660 are coupled toground through two switches 662 and 664, respectively. The apparatus ofFIG. 13 operates as follows: for the 1900 MHz operation, switch 662 isclosed and switch 664 is open; impedance networks 654 and 656 andcapacitor 658 operate in conjunction with stage 652 to providepredetermined, desired output impedance for the 1900 MHz operation. For800 MHz operation, switch 662 is open and switch 664 is closed, and thetwo impedance networks and capacitor 664 operate in conjunction withstage 652 to provide predetermined, desired output impedance for the 800MHz operation.

As will be apparent to those skilled in the art, numerous modificationsmay be made within the scope of the invention, which is not intended tobe limited except in accordance with the following claims.

What is claimed is:
 1. Amplifying apparatus for amplifying a signalhaving a frequency of one of a plurality of predetermined frequenciescomprising:at least one amplifying stage for amplifying such signal;input impedance means for providing, in accordance with the frequency ofsuch signal, predetermined input impedance at the frequency of suchsignal; and output impedance means for providing, in accordance with thefrequency of such signal, predetermined output impedance at thefrequency of such signal, the output impedance means comprising meansfor selectively coupling, in accordance with the frequency of suchsignal, a selected one of a plurality of output impedance networks tothe output of the amplifying stage.
 2. Amplifying apparatus foramplifying a signal having a frequency of one of a plurality ofpredetermined frequencies comprising:at least one amplifying stage foramplifying such signal; input impedance means for providing, inaccordance with the frequency of such signal, predetermined inputimpedance at the frequency of such signal; and output impedance meansfor providing, in accordance with the frequency of such signal,predetermined output impedance at the frequency of such signal, theoutput impedance means comprising means for controlling, in accordancewith the frequency of such signal, the impedance of an impedance networkcoupled to the output of the at least one amplifying stage. 3.Amplifying apparatus for amplifying a signal having a frequency of oneof a plurality of predetermined frequencies comprising:a plurality ofamplifying stages arranged as a cascade for amplifying such signal:input impedance means for providing, in accordance with the frequency ofsuch signal, predetermined input impedance at the frequency of suchsignal; and interstage impedance means for providing predeterminedimpedance between two successive amplifying stages at the frequency ofthe selected signal.
 4. The amplifying apparatus of claim 3 wherein theinterstage impedance means for providing predetermined impedance betweentwo successive amplifying stages comprise means for selectivelycoupling, in accordance with the frequency of such signal, one of aplurality of impedance networks connected a proceeding amplifying stageto a dc power supply.
 5. The amplifying apparatus of claim 3 wherein theinterstage impedance means for providing predetermined impedance betweentwo successive amplifying stages comprise means for controlling, inaccordance with the frequency of such signal, the impedance of animpedance network connected between a proceeding amplifying stage of thetwo successive amplifying stages and a dc power supply.
 6. Theamplifying apparatus of claim 5 wherein the impedance network connectedbetween a proceeding amplifying stage and a dc power supply comprisesand an inductor and a transistor connected in parallel, and the meanscontrols the impedance of the impedance network by controlling theconductivity of the transistor.
 7. Amplifying apparatus for amplifying asignal having a frequency that is one of a plurality of predeterminedfrequencies comprising:at least one amplifying stage; a plurality ofinput impedance networks for coupling to input of the at least oneamplifying stage, each of the input impedance networks, when coupled tothe input of the at least one amplifying stage, operating with the atleast one amplifying stage to provide predetermined impedance at one ofsuch predetermined frequencies; input impedance switching means forswitchably coupling one of the input impedance means that operates withthe at least one amplifying stage to provide predetermined impedance atthe frequency of such signal to the input of the at least one amplifyingstage.
 8. The amplifying apparatus of claim 7 further comprisingaplurality of output impedance networks for coupling to output of the atleast one amplifying stage, each of the output impedance networks, whencoupled to the output of the at least one amplifying stage, operatingwith the at least one amplifying stage to provide predeterminedimpedance at one of such predetermined frequencies; output impedanceswitching means for switchably coupling one of the output impedancemeans that, when coupled to the output of the at least one amplifyingstage, operates with the at least one amplifying stage to providepredetermined output impedance at the frequency of such signal, to theinput of the at least one amplifying stage.
 9. The amplifying apparatusof claim 7, comprising a plurality of amplifying stages arranged as acascade, the amplifying apparatus further comprising interstageimpedance means for providing predetermined impedance between twosuccessive amplifying stages at the frequency of the selected signal.10. A method for forming an amplifying apparatus for amplifying inputsignal having a frequency that is one of a plurality of predeterminedfrequencies or frequency bands, comprising the step of:coupling input ofan amplifying stage to a selected one of a plurality of input impedancenetworks each, when coupled to the input of the amplifier, operatingwith the amplifying stage to provide predetermined input impedance atone of the plurality of predetermined frequencies or frequency bands,the selected one input impedance network operating with the amplifyingstage to provide predetermined input impedance at the frequency of suchinput signal.
 11. The method of claim 10 further comprising the step ofcoupling output of an amplifying stage to a selected one of a pluralityof output impedance networks, each of the output impedance networks,when coupled to the output of the amplifier, operating with theamplifying stage to provide predetermined output impedance at one of theplurality of predetermined frequencies or frequency bands, the selectedone output impedance network operating with the amplifying stage toprovide predetermined output impedance at the frequency of such inputsignal.